Heads up display of information needed by a person looking through eyepieces is known to be convenient so that the viewer can get the necessary information without looking away from the viewing field. Besides eliminating the interruptive delay in moving back and forth between eyepieces and a separate meter reading, a heads up display is especially convenient for users who normally wear eyeglasses but remove them for viewing through adjusted eyepieces. Turning away from the field of view to observe a meter reading without eyeglasses can add to the delay.
Lensmeters for measuring the diopter value of eyeglasses have included a heads up display of the measured value derived from an engraved scale built into the instrument and lighted so that its reading is imaged in the apparent field of view. The engraving can be made small enough to make the numbers occupy a reasonably small portion of the apparent field.
For instruments that are controlled remotely from a microscope, an optomechanical engraving showing a control setting is not practical. Microsurgery accomplished with a microscope and a surgical laser presents this problem. Laser control settings must be viewed by the surgeon who is otherwise occupied with the surgical field of view available through microscope eyepieces. A heads up display of laser control settings within the apparent field of view of the microscope would be very convenient to the surgeon, but practical problems have stood in the way of a solution.
For example, an electronic digital display of numbers relevant to a control setting for a remote instrument cannot be imaged directly within the apparent field of a microscope binocular without consuming too much space. Even the small LED's used in hand-held calculators would fill more than half the apparent field of view if as few as three digits were directly displayed. Optically halving the image size of a small LED compatibly with binocular objectives having focal lengths ranging from 100 to 125 millimeters would require a collimating lens with a focal length of around 200 millimeters. A heads up display containing a lens with a 200 millimeter focal length would make the microscope unwieldy and interfere with the reach of the surgeon, even if the path were folded in half.
I have devised a compact and effective way of displaying control information from a remote instrument within the apparent field of view of a microscope so that the displayed information is suitably sized and positioned, and the system is compactly fitted within conventional microscopes. My system uses a beam splitter positioned in the essentially collimated light region between a microscope objective and image viewing binoculars, and I dispose a heads up display system adjacent the beam splitter where it does not take space away from the person using the microscope. My heads up display aims at convenience, compactness, efficiency, and reliability in presenting information from a remotely controlled instrument to the user of a microscope.